Hexane conversion

ABSTRACT

A process for producing isopentane which comprises: (a) isomerizing a C6rich fraction in an isomerization zone to obtain at least isopentane and C6 alkanes, (b) fractionating the isopentane from the C6 alkane to obtain an isopentane product, (c) disproportionating at least a portion of the C6 alkanes in a C6 disproportionation zone to obtain at least n-pentane and C7 hydrocarbons, and (d) isomerizing the n-pentane in the isomerization zone. Preferably, the isomerizing zone uses a sulfactive isomerization catalyst so that the isomerization zone serves not only an isomerization function but also a purification function for subsequent disproportionation. Normal butane produced in the C6 disproportionation zone is preferably disproportionated in a separate disproportionation zone to produce normal pentane which is isomerized to isopentane. It is particularly preferred to further integrate the disproportionation with the isomerization using common fractionation facilities.

limited States Patent Sieg 1 Feb. 27, 1973 [5 HEXANE CONVERSION PrimaryExaminerDelbert E. Gantz r Assistant Examiner-J. M. Nelson t P. P t [75]Inventor Robe? slag ledmon Calif Att0meyG. F. Magdeburger, R. H. Davies,T. G. De [73] Assignee: Chevron Research Company, San Jonghe and J, A.Buchanan, Jr.

. francisco, Calif. 22 Filed: Jan. 18, 1971 {57] ABSTRACT [21] Appl. No:107,207 A process for produc ng rsopentane which comprises: (a)rsomerrzmg a C rich fraction in an rsomerizatlon zone to obtain at leastisopentane and C alkanes, (b) [52] U.S. Cl. ..260/676 R, 260/683.65,260/683 D 'fractionating the isopentane from the C alkane to ob- [51]Int. Cl ..C07c 9/00 tain an isopentane product, (c) disproportionatingat [58] Field of Search ..260/676, 683.65 least a portion of the Calkanes in a C disproportionation zone to obtain at least n-pentane andC, [56] References Cited hydrocarbons, and (d) isomerizing the n-pentanein the isomerization zone. Preferably, the isomerizing UNITED STATESPATENTS zone uses a sulfactive isomerization catalyst so that 2 951 8889/1960 Carr...-. ..260/683.65 the isomerization Zone Serves iSOmeriZa'3:409: 2 11 19 Mitsche 2 0 tion function but also a purificationfunction for sub- 3,507,931 4/1970 Morris et al ....260/683.65 sequentdisproportionation. Normal butane produced 3,445,541 5/1969l-leckelsberg ..260/683 D in the C disproportionation zone is preferablydispro- 3,392,212 7/1968 DOuville ....260/683.73 portionated in aseparate disproportionation zone to 3,301,917 1/1967 Wise ....260/683.65produce normal pentane which is isomerized t0 v3,516,925 Lflwl'ence et-208/211 isopentane. It is particularly preferred to further in-3,676,522 7/1972 Slag ..260/683.65 tegrate the disproportionation withthe isomerization using common fractionation facilities.

14 Claims, 1 Drawing Figure x4 (15- TO LPG AND FUEL. i 6 V 6DISPROPORTIONATION 4 2 3 1a 3 z ISOPENTANE PRODUCT o 7 L sfie y ,2 2

ISOMERIZATION I n PENTANE r O U Q 9 1; LL

l a DISPROPORTIONATION 22 2; 20/ c1+ TO CAT REFORMING HEXANE CONVERSIONBACKGROUND OF THE INVENTION The present invention relates to acombination process involving isomerization of saturated hydrocarbons.More particularly, the present invention relates to isomerizationoperated in combination with saturated hydrocarbon disproportionation,and preferably with integrated common fractionation facilities.

isomerization is a well-known and frequently used step in petroleumrefining. It enables the adjustment of the octane number upwards byconverting normal paraffins, such as normal hexane, to isoparaffins,such as 2,2-dimethylbutane. A blend of various isomeric paraffinsprovides a gasoline which has a higher octane number than a gasolineconsisting of normal paraffins. isomerization is generally performed bypassing isomerizable hydrocarbons together with hydrogen through areaction zone containing an isomerization catalyst. Thehydrogen-to-hydrocarbon mol ratio varies within a wide range, generallyfrom 0.05:1 to :1, preferably within the range of about 0.5:1 to 2:1 forpentanes and hexanes and 0.1 :l to 1:1 for butanes. The reactiontemperature will depend upon the specific hydrocarbons being isomerizedand the nature and type of catalyst employed. Hydrocarbon streamsconsisting chiefly of pentanes and hexanes are usually isomerized attemperatures within the range of 200-900F. The isomerization, normallyeffected under pressure, may be carried out in the liquid or vaporphase. Generally, pressures within the range of 300-1000 psig have beenused. A liquid hourly space velocity (LHSV), that is, the volume ofliquid charged per hour per volume of catalyst, within the range of 0.5to 10.0 and preferably within the range of about 0.75 to 4.0 isemployed.

Various catalysts have been suggested for use in isomerizationprocesses. In general, the isomerization can be effected at lowtemperatures (ca. 300F.) with a Friedel-Crafts catalyst, such asaluminum chloride, or at high temperatures (ca. 750F.) with a supportedmetal catalyst, such as platinum on halogenated alumina orsilica-alumina. Thermodynamic equilibrium for isoparaffins is morefavorable at low temperatures; however, the low-temperature process hasnot received wide application because the. Friedel-Crafts catalyst isquite corrosive and therefore expensive metals or alloys must be used.Of the high temperature isomerization processes, the noble metalcatalysts such as platinum or palladium are perhaps considered to be themost effective.

As indicated in U.S. Pat. Nos. 2,951,888 and 3,472,912, minor amounts ofsulfur compounds in the feed to isomerization processes are harmful forthe typical isomerization processes. Catalysts used in typicalisomerization processes include composites of a hydrogenating componenton an amorphous acidic silica-alumina support and more usuallycomposites comprising halogenated alumina or aluminum, either of whichlatter composites are herein referred to as halogenated aluminumcatalysts.

According to U.S. Pat. No. 2,951,888, a C -C paraffinic feedstock isdesulfurized to a sulfur content less than 1 ppm so that better resultsare achieved in hydroisomerization of the paraffiuic feedstock with acatalystselected from the group consisting of nickel,

nickel-molybdenum, and palladium, supported on an acidic silica-aluminasupport containing 50-90 percent silica, at a temperature of 650-800F.,pressure of -1000 psig, and hydrogen-hydrocarbon m0] ratio of 0.5-5.0.

U.S. Pat. No. 3,472,912 also discloses an over-all combination processinvolving hydrotreating and isomerization wherein a nickelmolybdenum-on-alumina catalyst is used under hydrotreating conditions toremove sulfur from C -C saturated hydrocarbons so that the hydrocarbonscan be isomerized with increased life for the isomerization catalyst.Preferred isomerization catalysts according to the process of U.S. Pat.No. 3,472,912 are platinum-alumina composites activated by the additionof carbon tetrachloride (thereby resulting in a catalyst which is hereinclassified as a catalyst containing halogenated aluminum).

Recently, catalysts comprising either natural or synthetic crystallinealuminosilicates have been suggested for isomerization processes.Included among the crystalline aluminosilicates which have beensuggested are the type X and type Y silicates, mordenite, and layeredaluminosilicates such as described in Granquist U.S. Pat. No. 3,252,757.

U.S. Pat. No. 3,507,931, titled isomerization of Paraffmic Hydrocarbonsin the Presence of a Mordenite Catalyst discloses the isomerization ofstraight run distillates rich in C -C normal paraffms using a catalysthaving a high silica-to-alumina ratio, preferably above 20:1, andoperating the isomerization reaction at relatively low temperatures,such as 250-400F.

U.S. Pat. Nos. 3,280,212 and 3,301,917 also disclose hydroisomerizationprocesses using crystalline aluminosilicate-type catalysts.

As indicated above, the present invention is directed to bothisomerization and disproportionation.

The term disproportionation is used herein to mean the conversion ofhydrocarbons to new hydrocarbons of both higher and lower molecularweight. For example, butane may be disproportionated according to thereaction:

As can be seen from the above disproportionation reaction, the butane isin part converted to a higher molecular weight hydrocarbon, namely,pentane. Various processes have been suggested for convertinghydrocarbons to higher molecular weight hydrocarbons.

U.S. Pat. No. 1,687,890 is directed to a process of convertinglow-boiling-point hydrocarbons into higherboiling-point hydrocarbons bymixing a hydrocarbon vapor with steam and then contacting thesteamhydrocarbon mixture with iron oxide at temperatures in excess of1ll2F. It is theorized in U.S. Pat. No. 1,687,890 that the followingreactions may be involved to a greater or lesser extent:

"1. Paraffin hydrocarbons on being brought into contact with ferricoxide at elevated temperatures are oxidized or dehydrogenated, formingunsaturated hydrocarbons.

2. Unsaturated hydrocarbons of low molecular weight polymerize intounsaturated hydrocarbons of higher molecular weight when subjected toelevated temperatures, the extent of polymerization depending upon thetemperature and duration of treatment.

7. Unsaturated hydrocarbons are hydrogenated by nascent hydrogen.

Another process which has been proposed for converting hydrocarbons tohigher molecular weight hydrocarbons is olefin disproportionation.Numerous methods and catalysts have been disclosed for thedisproportionation of olefins. In most of these processes, the olefin isdisproportionated by contacting with a catalyst such as tungsten oxideor molybdenum oxide on silica or alumina at a temperature between about150-1100F. and at a pressure between about and 1500 psia. These priorart processes have been directed to an effective method to convertessentially only olefins, not saturated hydrocarbons, to highermolecular weight hydrocarbons by disproportionation.

For example, in U.S. Pat. No. 3,431,316, an olefin disproportionationprocess is disclosed, and it is stated that, if desired, paraffmic andcycloparaffinic hydrocarbons having up to 12 carbon atoms per moleculecan be employed as diluents for the reaction; that is, the saturatedhydrocarbons are non-reactive and merely dilute the olefins which arethe reactants.

A process for the direct conversion of saturated hydrocarbons to highermolecular weight hydrocarbons would be very attractive because in manyinstances saturated hydrocarbons are available as a relatively cheapfeedstock. For example, in many instances, excess amounts of propaneand/or butanes are available in an over-all refinery operation.

Processes which have been previously reported wherein saturatedhydrocarbons are disproportionated include contact of saturatedhydrocarbons with solid catalyst comprised of AlCl on A1 0 and contactof saturated hydrocarbons with a promoter comprised of alkyl fluorideand BF The use of the MCI, solid catalyst was uneconomic because, amongother reasons, the catalyst was non-regenerable. The use of alkylfluoride and BF was unattractive because of severe corrosion, sludgeformation and other operating problems.

In the past it has been the practice to convert saturated hydrocarbons,particularly normal alkanes, to olefins as a separate or distinct stepand then to disproportionate the olefins to valuable higher molecularweight hydrocarbons.

For example, in U.S. Pat. No. 3,431,316, saturated light hydrocarbonsare cracked to form olefins, and then the olefins are separated from thecracker effluent and fed to a disproportionation zone wherein theolefins are disproportionated to higher molecular weight hydrocarbons.Thus, a separate step is used to obtain olefins because, according tothe prior art, no economically feasible process is available for thedirect disproportionation of saturated hydrocarbons.

U.S. Pat. No. 3,445,541 discloses a process for thedehydrogenation-disproportionation of olefins and paraffins, using acombined dehydrogenation and disproportionation catalyst. According toU.S. Pat. No. 3,445,541, a hydrocarbon feed which is either an acyclicparaffin or acyclic olefin having 3-6 carbon atoms is contacted with thecatalyst at conditions of temperature and pressure to promotedehydrogenation and disproportionation. It is said that the process canbe carried out at temperatures between 800F. and 1200F.; however, thelowest temperature used for processing a paraffin in accordance with anyof the examples of U.S. Pat. No. 3,445,541 is 980F., and typically thetemperature used is between 1040F. and 1125F.

The high-temperature process disclosed in U.S. Pat. No. 3,445,541 isshown therein to result in only relatively low yields of saturatedhigher molecular weight hydrocarbons. The U.S. Pat. No. 3,445,541process operates with a substantial amount of olefins in the reactionzone and with about 10 to 50 volume percent or more olefins in theeffluent from the disproportionation reaction zone. U.S. Pat. No.3,445,541 does not disclose or suggest any advantages fordisproportionation of hexanes and butanes in combination with C and Cisomerization.

SUMMARY OF THE INVENTION According to the present invention, a processis provided for producing isopentane which comprises: (a) isomerizing aC -rich fraction in an isomerization zone to obtain at least isopentaneand C alkanes, (b) fractionating the isopentane from the C alkanes toobtain an isopentane product, (c) disproportionating at least a portionof the C alkanes in a C disproportionation zone to obtain at leastn-pentane and C hydrocarbons, and (d) isomerizing the n-pentane in theisomerization zone.

The process of the present invention results in the production ofhigh-octane isopentane from low-octane hexane (such as normal hexane,which has an octane rating of about 26). The isopentane which isproduced in the process of the present invention has an octane rating ofabout 92 and is particularly useful in high-octane unleaded orlow-lead-content gasolines.

Isomerization of C hydrocarbons can be used to upgrade the octane ratingof normal hexane-rich hydrocarbon fractions. However, the octane can beincreased only to about -75 (motor octane) by isomerization because themain hexane isomers produced, namely, 2-methyl pentane and 3-methylpentane, have an octane rating of only 73 and 75, respectively. Althoughincreasing the octane rating of a C fraction from the vicinity of about26, which is the octane of normal hexane, to about 70-75 byisomerization to produce isohexanes represents a substantial increase,it is generally not a sufficient increase to produce highoctane gasolinecomponents for use in unleaded or lead-free gasolines.

The C -rich hydrocarbons also have been considered as feedstocks forcatalytic reforming in order to reform the C material into reasonablylow volatility gasoline boiling range hydrocarbons in the octane range.However, the C hydrocarbons have been found to make a relativelyunattractive feedstock for catalytic reforming processes.

Thus, it is desirable to provide a process for upgrading C -richhydrocarbon fractions into 90+ octane rating components. The process ofthe present invention achieves these desired results by the combinationof isomerization with disproportionation. In addition, the isomerizationstep is particularly advantageously employed with the disproportionationstep in the present invention as the isomerization step serves the dualfunction of (l) purifying C rich hydrocarbons which are subsequentlydisproportionated, and (2) isomerizing a portion of the C hydrocarbons.

The isomerization zone serves to purify the feed for thedisproportionation zone by converting sulfur compounds in the C -richfeed to the isomerization zone to hydrogen sulfide, which can be readilyremoved from the isohexane-rich effluent from the isomerization zonebefore the isohexane-rich effluent is fed to the disproportionationzone. The preferred catalyst used in the disproportionation zone issensitive to even small amounts of H 8, and H 8 will be formed in thedisproportionation zone unless the organic sulfur compounds aresubstantially completely removed ahead of the disproportionation zone.

Also, the isomerization zone can serve to increase the amount ofisopentane produced in the disproportionation zone by providing abranched-chain C feed for the disproportionation zone. Using thepreferred dual-function dehydrogenation-olefin disproportionationcatalyst for the disproportionation zone, there is substantially noproduction (or depletion) of branchedchain hydrocarbons in thedisproportionation reaction zone.

According to a preferred embodiment of the present invention, theisomerization zone is further integrated with the disproportionationzone by using common fractionation facilities, at least in part. Theterm fractionation facilities is used herein to mean distillationcolumns or the like and associated equipment.

The effluent from the C -C isomerization zone is usually composedprimarily of isopentane, normal pentane, isohexanes and normal hexane.However, there also is present minor or small amounts of propane,isobutane, normal butane and C-,+ hydrocarbons. It will, of course, beunderstood that the amount of these secondary hydrocarbons will dependupon several factors, including the composition of the feed to theisomerization zone, the type catalyst used in the isomerization zone(some isomerization catalysts have higher per-pass conversions but lowerselectivities to the desired isopentane and isohexane products), and thetemperature used in the isomerization zone (higher temperaturesusually'resulting in more light hydrocarbons such as propane andbutanes). The effluent hydrocarbons from normal hexanedisproportionation according to the preferred embodiments of the presentinvention using the two-component disproportionation catalyst usuallyare primarily propane, normal butane, normal pentane, normal hexane andC hydrocarbons. However, there will also be minor or small amounts ofisobutane, isopentane, and isohexane. The amounts of these isoorbranched-chain hydrocarbons will increase if increased amounts ofisohexane are fed to the C disproportionation step. Thus, it isparticularly advantageous to use common fractionation facilities for theisomerization zone effluent hydrocarbons and the disproportionation zoneeffluent hydrocarbons when substantial amounts, for example more than 5or 10 weight percent, isohexane is fed to the C disproportionation zonebecause, in this instance, there is an increased'amount of commonhydrocarbons from both the isomerization zone and the disproportionationzone.

The fractionation facilities required for the effluent from theisomerization zone and for the effluent from the disproportionation zonecan range from one or two columns up to about 8 sequential columns. Forexample, a propane splitter to separate propane from isobutanel; anisobutane splitter to separate isobutane from normal butane+; a normalbutane splitter to separate normal butane from isopentane+; anisopentane splitter to separate isopentane from n-pentane+; a normalpentane splitter to separate normal pentane from isohexane+; anisohexane splitter to separate isohexane from normal hexane+; and anormal hexane splitter to separate normal hexane from C Thefractionation of the aforementioned hydrocarbon cuts can be carried outin sequential separate columns or, at the other extreme, one column canbe used similar to crude oil distillation with side streams beingwithdrawn from the column and stripped, if necessary. As indicatedpreviously, the amounts of the various components present in theeffluents from the isomerization zone and the disproportionation zonecan vary. Thus, in some instances, only part of the fractionation forthe two zones will be carried out in common fractionation facilitieswith the other part being carried out in separate fractionationfacilities for the respective zones. Because there are usuallysubstantial amounts of normal pentane and C alkanes in the effluenthydrocarbons in both the isomerization zone and the disproportionationzone, it is particularly preferred to carry out the separation of normalpentane from C alkanes in a distillation column common to both theisomerization zone and the disproportionation zone.

In the process of the present invention, the feed to the Cdisproportionation zone can be a normal hexane feed or a feed containingsubstantial amounts of isohexane in addition to normal hexane. Usuallyit is preferred to feed the isohexane as well as the normal hexane tothe disproportionation zone so as to produce isopentane (as well asnormal pentane from the normal hexane). isopentane has a substantiallyhigher octane than the isohexanes Z-methyl pentane and 3-methyl pentane,which are the primary isohexane products from C isomerization usingsulfactive isomerization catalysts and isomerization conditions(500800F.) suitable for hydrodesulfurization.

As indicated above, one of the important purposes which theisomerization zone serves in the process of the present invention is toremove sulfur impurities from the C fraction before the C fraction isfed to the disproportionation zone. in broad scope, the process of thepresent invention can be applied to the isomerization and subsequentdisproportionation of C -rich hydrocarbon streams which are essentiallyfree of sulfur impurities as, for example, C hydrocarbon streamsobtained from a catalytic reforming unit. However, the processcombination of the present invention has particular advantage whenapplied to C -rich hydrocarbon streams containing minor amounts ofsulfur impurities,

usually at least 5 ppm sulfur.

C hydrocarbon cuts obtained by crude oil distillation, i.e., straightrun C -rich hydrocarbon fractions, contain usually at least 5 ppmorganic sulfur compounds (calculated as elemental sulfur by weight) andgenerally between about 20 and 500 ppm organic sulfur compounds. Theisomerization zone can use a hydrotreating step ahead of theisomerization reaction zone catalyst as in the case of using halogenatedaluminum-type catalysts, but it is preferred in the process of thepresent invention to use a crystalline aluminosilicate-typehydroisomerization catalyst, many of which catalysts we have found canbe operated with several hundred ppm sulfur and frequently up to about500 or 1000 ppm sulfur in the feed without substantially decreasing thelife of the hydroisomerization catalyst. Also, the crystallinealuminosilicate-type catalyst can be used to obtain relatively highyields of isohexane per pass at temperatures usually about 100F. lessthan is required for a comparable isohexane yield using halogenatedaluminum-type isomerization catalysts. Halogenated aluminum-typecatalysts which are sensitive to sulfur poisons and thus not aspreferred for use in the process of the present invention include thecatalyst such as used in the butamer process described in the Oil andGas Journal, Vol. 56, No. 13, Mar. 31, 1958, pp. 73-76, the BPisomerization process as described in Hydrocarbon Processing, Vol. 45,No. 8, August 1966, pp. 168-170, and the liquid phase isomerizationprocess described in Hydrocarbon Processing, Vol. 42, No. 7,Julyl963,pp. 125-130.

Thus, in the process of the present invention, it is preferred to use ahydroisomerization catalyst which is essentially free of halogenatedaluminum. Catalysts comprising crystalline aluminosilicates, such asmolecular sieves, mordenite, and layered crystalline aluminosilicates,are particularly preferred. It is preferred to use one or morehydrogenation components with the crystalline aluminosilicate. Palladiumand platinum are preferred hydrogenation components. Preferred catalystscomprising crystalline aluminosilicate and a hydrogenation componentsuch as palladium or others are described in patent applications Ser.Nos. 776,733 and 839,999, which applications are incorporated byreference into the present patent application, particularly thoseportions of the afore-identified applications disclosing catalystcompositions. Preferred aluminosilicate-containing catalysts for use inthe isomerization zone include catalysts comprising a layered clay-typealuminosilicate cracking component, with 0.01 to 2.0 weight percent,based on said cracking component and calculated as the metal, of ahydrogenating component selected from platinum, palladium, iridium,ruthenium, and rhodium, and also with 0.01 to 5.0 weight percent, basedon said cracking component and calculated as the metal, of ahydrogenating component selected from tungsten and chromium.Particularly preferred hydroisomerization catalysts are those asdescribed above wherein the hydrogenating components are palladium andchromium. In the present specification, oxides and other compounds ofmetals are to be considered as included in reference to a metal simplyas an element, i.e., chromium includes the use of chromium in compoundforms such as chromium oxide.

The C disproportionation zone operated in accordance with the presentinvention in combination with the C -C isomerization zone will usuallyproduce substantial amounts of butanes in addition to thedisproportionation of hexane to pentane and heptane. Butane is producedin accordance with the following disproportionation reaction:

Butanes have a high octane rating with normal butane having an octanerating of about and isobutane having an octane rating of about 99.However, only limited amounts of butanes can be used in motor gasolinesbefore exceeding Reid Vapor Pressure limitations for the gasoline.

Thus, it is particularly preferred in the process of the presentinvention to upgrade butanes produced in the C disproportionation zoneto high-octane gasoline boiling range hydrocarbons which are not asvolatile as the C, hydrocarbons. ln accordance with a particularlypreferred embodiment of the present invention, this objective isaccomplished by operation of a separate butane disproportionation zonein combination with the isomerization zone and the C disproportionationzone. The butane fed to the C, disproportionation zone is at least inpart derived from the butanes resulting from the C disproportionation.The butanes are disproportionated in the butane disproportionation zoneto obtain increased amounts of normal pentane, which is in turn fed atleast in part to the isomerization zone to produce the high-octane,relatively low-volatility product, isopentane.

Although the butane disproportionation is preferably carried out in thesame plant as the plant used for the hexane disproportionation step,usually, and preferably, separate reactors are used for the Cdisproportionation and the C disproportionation, respectively.

Preferred catalysts for use in both the C and the C, disproportionationreaction zones are catalytic masses having a component with alkanedehydrogenation activity and a second component with olefindisproportionating activity, for example, catalytic masses comprising aGroup VIII metal component and a Group VIB metal component. Particularlypreferred disproportionation catalysts include catalytic massescomprising a noble metal on a refractory support and a Group VIB metalor metal compound on a refractory support, for example a catalytic masscomprising platinum on alumina and tungsten or tungsten oxide on silica.Preferred temperatures for the disproportionation of normal butane andfor the disproportionation of C alkanes using the above-indicatedcatalytic masses are between about 400-850F. and more preferably between650-799F. Pressure maintained in the disproportionation reaction zone ispreferably between atmospheric and 2500 psia, and still more preferablybetween and 1500 psia. In addition to the preferred relatively lowtemperature for hydrocarbon disproportionation, we have-found that it ispreferable to carry out the disproportionation reaction in the presenceof no more than a few weight percent olefins, preferably less than 5weight percent olefins. Preferred conditions for the disproportionationof saturated hydrocarbons such as butane or hexane are further discussedin commonly assigned applications Ser. Nos. 3,303 and 3,306, thedisclosures of which applications are incorporated by reference into thepresent application.

Thus some of the important advantages obtained in accordance withparticularly preferred embodiments of the present invention include: (1)using sulfactive isomerization catalysts, particularly layered clay-typecatalysts as described above, sulfur-containing C hydrocarbon feed tothe process can be desulfurized while it is being isomerized; (2) theisomerization zone is used both for C isomerization and also for theisomerization of normal pentane to isopentane; (3) in utilizing separateC and C disproportionation reactors in the preferred embodiment asdescribed above, the separate disproportionation steps can be operatedat the best temperature, space rates and other operating conditions fortheir respective feeds, whereas if C and C alkanes are interactedtogether in an averaging reaction, it is necessary to select the bestcompromise operating conditions; (4) in addition to the Cdisproportionation zone handling the problem of some C product from theC disproportionation zone, the C disproportionation zone isadvantageously used to handle the problem of some C alkane product fromthe C disproportionation zone. Thus, each disproportionation reactortakes care of a selectivity problem for the other reactor. For example,two C s go mainly to a C and a C but they do go partly to a C 4 and a Calkane. Conversely, two C s go mainly to a C and a C but do go partly toC and C alkanes; (5) common fractionation facilities can be used tofurther integrate the disproportionation zone or zones with theisomerization zone. The common fractionation facilities reduce the costof separating the respective components, reduce the complexity of thecombination and make it easier to route undesired products to the properplace to convert them at least partly to the proper product toultimately produce the desired isopentane product.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic process flowdiagram illustrating preferred embodiments of the present invention.

DETAILED DESCRIPTION OF THE DRAWING Referring now more particularly tothe drawing, a C -rich hydrocarbon stream is fed via lines 1 and 3 toisomerization zone 4. The C fraction or cut can be obtained from theeffluent from a catalytic reforming process and advantageously upgradedin the process of the present invention to isopentane. However, theprocess combination of the present invention has particular applicationto straight run hydrocarbon C -rich fractions containing organic sulfurcompounds, usually in an amount between about 5 ppm and 300 ppm,calculated as'sulfur by weight.

The C -rich hydrocarbon fraction is isomerized in the presence ofhydrogen using a hydroisomerization catalyst which preferably comprisesa crystalline aluminosilicate together with a hydrogenation componentsuch as palladium or platinum. Preferred operating conditions for the Cisomerization include a hydrogen gas rate in the range of 1000 to 5000SCF/b., preferably 1500 to 2000 SCF/b.; space velocities in the range ofabout 0.1 to liquid volumes per hour per volume of catalyst, preferably1.0 to 5.0 LHSV; temperatures in the range of about 200-800F.,preferably 250 to 750F.; and pressures within the range of atmosphericto 3000 psig, preferably in the range of 500-800 psig.

In addition to isomerizing normal hexane in isomerization zone 4, normalpentane derived from disproportionation zone 12 is also isomerized inzone 4. As shown in the drawing, normal pentane from thedisproportionation zone is recycled via line 2 and then introduced vialine 3 to the isomerization zone. After stripping hydrogen sulfide fromthe isomerization reaction zone effluent, the isomerization effluenthydrocarbons are fed via lines 5 and 7 to fractionation zone 8.

Fractionation zone 8 typically consists of 3 to 8 distillation columnsused to separate the various components obtained both from isomerizationin zone 4 and disproportionation in zones 12 and 16, according to thepreferred embodiment illustrated in the drawing. As indicatedpreviously, the fractionation zone can have a varying number ofdistillation columns, and it is preferred to use common fractionationfacilities for at least part of the separation of effluent hydrocarbonsfrom isomerization zone 4 and disproportionation zone 12. It isparticularly preferred to carry out the fractionation of normal pentanefrom C alkanes in the same fractionation column for effluenthydrocarbons from disproportionation zone 12 and isomerization zone 4.

C alkanes are removed from the fractionation zone via line 9 and fed todisproportionation zone 12 via line 11. A portion of the C hydrocarbonsfrom the fractionation zone can be recycled back to the isomerizationzone instead of feeding all the C hydrocarbons to C disproportionation.

C hydrocarbons are disproportionated in zone 12 at least in part toobtain normal pentane and heptane. Effluent hydrocarbons includingnormal pentane are removed from disproportionation zone 12 via line 13and passed via lines 6 and 7 to fractionation zone 8.

In fractionation zone 8 normal pentane is separated. The normal pentaneis passed via line 2 and line 3 to isomerization zone 4.

In isomerization zone 4, the normal pentane derived fromdisproportionation zone 12 is isomerized to isopentane which isultimately fractionated from the isomerization zone effluenthydrocarbons and recovered asa product withdrawn via line 18.

Propane and other light gases formed in isomerization zone 4 and also indisproportionation zone 12 are removed from the effluent hydrocarbonsfrom these two respective zones by separation in zone 8. Preferably,common fractionation facilities are used to separate the propane andother light gases generated in disproportionation zones 12 and 16 and inisomerization zone 4, particularly when the isomerization is carried outat a high temperature, for example in excess of 700 or 750F., so as togenerate substantial amounts of propane and other light hydrocarbons.When the isomerization zone is operated at relatively mild conditions,for example below 700F., and-with only one or two percent or less weightpercent propane produced in isomerization zone 4, depropanizing theeffluent hydrocarbons from the isomerization zone could advantageouslybe carried out separate from the The data tabulated in Table II belowillustrate the results obtained in disproportionating normal butane bycontacting normal butane with an alkane disproportionation catalyst massunder the following conditions:

Volume of Catalyst in Reactor: 9 cubic centimeters (cc.) Type ofCatalyst:

2 cc. of 0.5 wt.% Pt; 0.5 wt. Re; 0.5 wt.% Lion Al a 7 cc of 8.0 wt.% Won SiO Both types of catalyst particles were 28 to 60 Tyler mesh size.

Operating Conditions:

Temperature: 650, 700, 750, 800, 875F. Pressure: 900 psig Feed rate: 9cc./hour Successive runs, of several hours each with no regeneration inbetween, were made at the temperatures specified, except that thecatalyst was reactivated by flushing the catalyst overnight withhydrogen before the run at 875F.

As can be seen from the data tabulated in Table ll, the ultimate yieldof C decreases considerably in moving from particularly preferredtemperatures below 800F. to temperatures in excess of 800F. as, forexample, temperatures as high as 875F., where the ultimate yield of Cdrops to about 42 percent vs. approximately 57 percent at 750F. Moreimportantly, the yield of nC is seen to be greater at temperaturesbetween 700 and 800F. than at higher temperatures such as 875F.

TABLE II Weight Product Yields at Various Operating Temperatures 12 arefed to disproportionation zone 16 for conversion in part to normalpentane, which in turn is converted in isomerization zone 4 tohigh-octane isopentane. Butanes are withdrawn via line 15 fromfractionation zone 8 and fed to disproportionation zone 16. Effluent 5hydrocarbons including normal pentane are withdrawn via line 17 andpassed via lines 6 and 7 to fractionation zone 8. The normal pentane iswithdrawn from fractionation zone 8 and passed via lines 2 and 3 toisomerization zone 4.

The disproportionation reaction in zones 12 and 16 is preferably carriedout in separate reactors, for example parallel reactors in a singledisproportionation plant. The preferred catalyst is a two-componentcatalyst comprising an alkane dehydrogenation component and an olefindisproportionation component.

Some heavier hydrocarbons, i.e., C,+ hydrocarbons, are formed in bothdisproportionation zone 12 and zone 16. These heavier hydrocarbons arewithdrawn from fractionation zone 8 via line 20. The C,+ hydrocarbonscan be advantageously used as a feedstock for catalytic reforming toproduce high-octane gasoline, for example by reforming using aplatinumrhenium on alumina catalyst. The C hydrocarbons alternately canbe passed at least in part via lines 22 and 11 to C disproportionationzone 12. The C-,+ hydrocarbons are suitable feedstock fordisproportionation to lower hydrocarbons including normal pentane.

EXAMPLES Example 1 A C -rich fraction was desulfurized from ppm S Allolefins analyses are from an approximate chromatographic analysis.

The decrease in branching with decreasing temperature indicate theprocess of the present invention is more selective for puredisproportionation without isomerization at lower temperatures. Thisattribute is important when it is desired to produce n-parafiins, as,for example, in wax production.

NM. not measured because products were hydrogenated prior to analysis.

Although various embodiments of the invention have been described, it isto be understood that they are meant to be illustrative only and notlimiting. Certain features may be changed without departing from thespirit or scope of the present invention. It is apparent that thepresent invention has broad application to combined C C alkaneisomerization and C disproportionation to produce isopentane.Accordingly, the

invention is not to be construed as limited to the specific embodimentsor examples discussed, but only as defined in the appended claims orsubstantial equivalents of the claims.

What is claimed is:

1. A process for producing isopentane which comprises:

a. isomerizing a C -rich hydrocarbon fraction containing C hydrocarbonsin an isomerization zone to obtain at least isopentane and C alkanes;

b. fractionating the isopentane from the C alkanes to obtain anisopentane product;

c. disproportionating at least a portion of the C alkanes in a Cdisproportionation zone by contacting the C alkane with a catalystcomprising a Group VIII metal or metal compound and a Group VIB metal ormetal compound at a temperature between 400F. and 850F. to obtain atleast npentane and C hydrocarbons; and

d. isomerizing the n-pentane to iso-pentane in the isomerization zone.

2. A process in accordance with claim 1 wherein the C -rich hydrocarbonfeed to the isomerization zone contains at least 5 ppm sulfur present asorganic sulfur compounds and the isomerization is carried out using asulfactive isomerization catalyst at conditions sufficient to convertthe organic sulfur compounds to l-l,S and hydrocarbons, and H 8 isseparated from the C alkanes from the isomerization zone before the Calkanes are fed to the disproportionation zone.

3. A process in accordance with claim 1 wherein C alkanes aredisproportionated in accordance with step (c) to obtain normal pentane,C hydrocarbons, and normal butane, and wherein the normal butane isdisproportionated in a C disproportionation zone to obtain at leastnormal pentane and propane, and wherein at least a portion of the normalpentane obtained by normal butane disproportionation is isomerized inthe isomerization zone.

4. A process in accordance with claim 1 wherein common fractionationfacilities are used at least inpart for effluent hydrocarbons from theisomerization zone and effluent hydrocarbons from the Cdisproportionation zone. 1

5. A process in accordance with claim 4 wherein the same fractionationcolumn is used for the fractionation of normal pentane from C alkanespresent as a mixture in effluent hydrocarbons from both theisomerization zone and the C disproportionation zone.

6. A process in accordance with claim 1 wherein the C -rich hydrocarbonstream fed to the isomerization zone is a straight run fraction obtainedby fractionating a C -rich cut from crude oil.

7. A process in accordance with claim 1 wherein the catalyst used in theisomerization zone is substantially free of halogenated aluminum.

8. A process in accordance with claim 1 wherein the isomerizationcatalyst comprises palladium or platinum and a crystallinealuminosilicate material.

9. A process in accordance with claim 1 wherein the isomerizationcatalyst comprises 0.05 to 5.0 weight percent palladium and 0.05 to 5.0weight percent chromium on a layered clay-type crystallinealuminosilicate material.

10. A process in accordance with claim 1 wherein the disproportionationreaction is carried out at a temperature between 400 and 850F. using acatalyst comprising a noble metal on a refractory support and a GroupVlB metal compound on a refractory support.

11. A process in accordance with claim 1 wherein the disproportionationreaction comprises contacting the C alkanes with a catalytic masscomprising platinum on alumina and tungsten or tungsten oxide on silicaat a temperature between about 650 and 850F. and a pressure betweenabout psia and 1500 psia.

12. A process in accordance with claim 11 wherein the olefinconcentration in the disproportionation reaction zone is maintainedbelow about 5 volume percent.

13. A process for producing isopentane from C hydrocarbons whichcomprises:

a. isomerizing a C -rich hydrocarbon stream containing between 5 and 500ppm organic sulfur compounds in an isomerization zone by contacting theC -rich hydrocarbons with a sulfactive isomerization catalyst at ahydrogen partial pressure between about 100 and 1500 psig and atemperature between about 200F. and 800F. to obtain a C -rich effluentstream containing less than 1 ppm sulfur present as organic sulfurcompounds,

. disproportionating at least a portion of the C -rich effluent streamby contacting the C hydrocarbons with a catalyst comprising platinum ona refractory support and a Group VIB metal or metal oxide on arefractory support at a temperature between 400 and 850F. to obtain ahydrocarbon stream comprising normal butane, normal pentane and Chydrocarbons,

c. disproportionating at least a portion of the normal butane in theeffluent from C disproportionation by contacting the normal butane witha catalyst comprising platinum on a refractory support and a Group VIBmetal or metal oxide on a refractory support at a temperature between400 and 850F. to obtain a stream containing propane and normal pentane,and

d. isomerizing at least a portion of the normal pentane from the c,disproportionation and at least a for the isomerization zone and the Cdisproportionation zone and the C disproportionation zone.

2. A process in accordance with claim 1 wherein the C6-rich hydrocarbonfeed to the isomerization zone contains at least 5 ppm sulfur present asorganic sulfur compounds and the isomerization is carried out using asulfactive isomerization catalyst at conditions sufficient to convertthe organic sulfur compounds to H2S and hydrocarbons, and H2S isseparated from the C6 alkanes from the isomerization zone before the C6alkanes are fed to the disproportionation zone.
 3. A process inaccordance with claim 1 wherein C6 alkanes are disproportionated inaccordance with step (c) to obtain normal pentane, C7 hydrocarbons, andnormal butane, and wherein the normal butane is disproportionated in aC4 disproportionation zone to obtain at least normal pentane andpropane, and wherein at least a portion of the normal pentane obtainedby normal butane disproportionation is isomerized in the isomerizationzone.
 4. A process in accordance with claim 1 wherein commonfractionation facilities are used at least in part for effluenthydrocarbons from the isomerization zone and effluent hydrocarbons fromthe C6 disproportionation zone.
 5. A process in accordance with claim 4wherein the same fractionation column is used for the fractionation ofnormal pentane from C6 alkanes present as a mixture in effluenthydrocarbons from both the isomerization zone and the C6disproportionation zone.
 6. A process in accordance with claim 1 whereinthe C6-rich hydrocarbon stream fed to the isomerization zone is astraight run fraction obtained by fractionating a C6-rich cut from crudeoil.
 7. A process in accordance with claim 1 wherein the catalyst usedin the isomerization zone is substantially free of halogenated aluminum.8. A process in accordance with claim 1 wherein the isomerizationcatalyst comprises palladium or platinum and a crystallinealuminosilicate material.
 9. A process in accordance with claim 1wherein the isomerization catalyst comprises 0.05 to 5.0 weight percentpalladium and 0.05 to 5.0 weight percent chromium on a layered clay-typecrystalline aluminosilicate material.
 10. A process in accordance withclaim 1 wherein the disproportionation reaction is carried out at atemperature between 400* and 850*F. using a catalyst comprising a noblemetal on a refractory support and a Group VIB metal compound on arefractory support.
 11. A process in accordance with claim 1 wherein thedisproportionation reaction comprises contacting the C6 alkanes with acatalytic mass comprising platinum on alumina and tungsten or tungstenoxide on silica at a temperature between about 650* and 850*F. and apressure between about 100 psia and 1500 psia.
 12. A process inaccordance with claim 11 wherein the olefin concentration in thedisproportionation reaction zone is maintained below about 5 volumepercent.
 13. A process for producing isopentane from C6 hydrocarbonswhich comprises: a. isomerizing a C6-rich hydrocarbon stream containingbetween 5 and 500 ppm organic sulfur compounds in an isomerization zoneby contacting the C6-rich hydrocarbons with a sulfactive isomerizationcatalyst at a hydrogen partial pressure between about 100 and 1500 psigand a temperature between about 200*F. and 800*F. to obtain a C6-richeffluEnt stream containing less than 1 ppm sulfur present as organicsulfur compounds, b. disproportionating at least a portion of theC6-rich effluent stream by contacting the C6 hydrocarbons with acatalyst comprising platinum on a refractory support and a Group VIBmetal or metal oxide on a refractory support at a temperature between400* and 850*F. to obtain a hydrocarbon stream comprising normal butane,normal pentane and C7 hydrocarbons, c. disproportionating at least aportion of the normal butane in the effluent from C6 disproportionationby contacting the normal butane with a catalyst comprising platinum on arefractory support and a Group VIB metal or metal oxide on a refractorysupport at a temperature between 400* and 850*F. to obtain a streamcontaining propane and normal pentane, and d. isomerizing at least aportion of the normal pentane from the C6 disproportionation and atleast a portion of the normal pentane from the C4 disproportionation inthe isomerization zone to obtain isopentane.
 14. A process in accordancewith claim 13 wherein common fractionation facilities are used at leastin part for the isomerization zone and the C6 disproportionation zoneand the C4 disproportionation zone.